I. Field of the Invention
The present invention relates to rubber compositions, and more particularly, to rubber compositions including one or more processing aids.
II. Description of the Related Art
Processing aids are commonly used in both natural and synthetic rubber compositions. Representative examples of processing aids include naphthenic oil, paraffinic oil, and aromatic oil. Such processing aids are used during mixing, thereby permitting fillers and other ingredients to be added more rapidly and with lower power consumption.
Despite these benefits, and depending on the particular rubber composition, such processing aids may end up extending the time required to cure a particular rubber composition. Also, such processing aids may adversely affect the performance of the resulting rubber product.
The present invention overcomes the above-mentioned drawbacks by providing a rubber composition which not only allows for rapid addition of fillers and other ingredients with lower power consumption, but also provides a faster cure rate, as well as improved tear resistance in the finished product.
One aspect of the invention is directed to a rubber composition which includes at least one sulfur-vulcanizable elastomer containing olefinic unsaturation, a first processing aid, and a second processing aid of the formula: 
wherein each of R1 and R2 independently is selected from the group consisting of alkyls having from 12 to 24 carbon atoms, and alkenyls having from 12 to 24 carbon atoms. The elastomer is present in an amount of 100 parts by weight. Also, the first processing aid may be present in an amount of 0 to 20 phr, and the second processing aid may be present in an amount of 0.2 to 20 phr.
Another aspect of the invention is directed to a method of processing the rubber composition described immediately above, with the method including the step of mixing the elastomer, first processing aid, and second processing aid.
With regard to the second processing aid, each of R1 and R2 may be an alkenyl having from 16 to 20 carbon atoms. Also, if desired, the second processing aid may be N,Nxe2x80x2-dioleoylethylenediamine (xe2x80x9cDOEDxe2x80x9d). The formula for DOED is as follows: 
If desired, the first processing aid may be selected from the group consisting of a naphthenic oil, a paraffinic oil, an aromatic oil, and combinations of such oils. With regard to the sulfur-vulcanizable elastomer, if desired, the elastomer may be a homo-, co-, or ter-polymer produced using a monomer selected from the group consisting of isoprene, butadiene, styrene, and combinations thereof.
In a further aspect, the composition may include a reinforcing filler. If desired, the reinforcing filler may be selected from the group consisting of carbon black, amorphous precipitated silica, starch, clay, and combinations thereof. The carbon black may be used in an amount of 20 to 100 phr, and the silica may be used in an amount of 0 to 30 phr.
The invention is directed to a rubber composition and method of making the rubber composition. The composition, itself, is a mixture of 100 parts by weight of at least one sulfur-vulcanizable elastomer containing olefinic unsaturation, a first processing aid, and a second processing aid of the formula: 
wherein each of R1 and R2 independently is selected from the group consisting of alkyls having from 12 to 24 carbon atoms, and alkenyls having from 12 to 24 carbon atoms. The first processing aid is present in an amount of 0 to 20 phr, and the second processing aid is present in an amount of 0.2 to 20 phr. This mixture of component ingredients provides several benefits and advantages. For example, the inclusion of the second processing aid results in a faster cure time, as well as a greater resistance to tearing in the resulting product.
The sulfur-vulcanizable elastomer containing olefinic unsaturation may be a homo-, co-, or ter-polymer made from any suitable, commercially-available monomer. For example, isoprene, butadiene, styrene, and combinations thereof may be used.
In similar fashion, the first processing aid may be any suitable, commercially-available processing aid. For example, the first processing aid may be a naphthenic oil, a paraffinic oil, and/or an aromatic oil.
With regard to the second processing aid, in one particular version of the invention, the processing aid may be a particular ethylenediamine derivative, namely N,Nxe2x80x2-dioleoylethylenediamine (xe2x80x9cDOEDxe2x80x9d). This particular ethylenediamine derivative has the structural formula: 
DOED is commercially available from Lonza Inc. under the trademark Glycolube VL(trademark).
The rubber composition may include other ingredients, as desired. For example, the mixture of ingredients may include one or more reinforcing fillers. For example, 20 to 100 phr of carbon black and/or 0 to 30 phr of amorphous precipitated silica may be used.